Many different applications in a real-time system involve making a decision from a prescribed set of data elements in a current decision situation. In this context, the set of data elements can also include discrete numbers. Information technology offers many kinds of solutions to such problems. One component is computer-related formulation of the selection, which is done using programming languages or using descriptions of selection devices and the associated tools.
There are two different approaches to describing the operation of a real-time system. A first description approach is operational, in which a program is written in the form of precise individual instructions whose execution is precisely stipulated. An example of the first description approach is programs written in a programming language such as the C programming language. A benefit of the first description approach is that through compilation efficient code can be produced. A drawback is that a skilled programmer is needed to write such programs, as users (e.g., administrators or operators of a real-time system, and even more so application experts of the considered real-time domain) generally cannot develop such programs. In addition, the actual effect of a program on the real-time system is typically not easy to comprehend, and the described function can often vary greatly in the case of small changes to the program. This makes creating and changing the description complicated. The second approach is predicative, which describes properties of the desired results and prescribes the flow of calculation indirectly. A benefit of the predicative approach is that users can deliver the description in special areas with appropriate support. With the predicative approach, however, a drawback is that the description usually takes much longer to execute than its operational description counterpart.
Typically, users can create only very simple operational descriptions without mistakes. However, the extended execution time for predicative descriptions is problematic in many respects. The predicative descriptions increase the expense of technical solutions for tasks which need to be carried out under real-time demands, or even make certain technical solutions unachievable.